The present invention relates to a motorbrake for a Diesel engine with engine breathing valves and a fuel injector mounted in each cylinder for injecting fuel supplied by a high pressure pump via a common rail distribution line, and means for operating a valve during an engine compression stroke by high pressure fuel from the common rail distribution line to provide for motor braking.
Motorbrake systems for commercial vehicle internal combustion engines with a motorbrake flap valve arranged in the exhaust pipe so as to be controllable for decelerating the vehicle are well known. It is also known to equip the engine with decompression valves which are maintained open during engine braking operation (constant-throttle valves) to thereby increase engine braking effectiveness.
DE 39 04 497 C1 discloses a decompression braking arrangement with a hydraulic operating device for actuating an exhaust valve by the fuel injection pump of the engine. For this purpose, the fuel pipe from the injection pump to the injector includes a control valve which blocks the fuel flow to the injector and provides a flow path to the hydraulic operating device for actuating the exhaust valve during the compression stroke of the engine.
Also known is a decompression brake arrangement wherein the engine is provided with a common high pressure fuel supply line (common rail) for supplying fuel to the various fuel injectors under the control of individual magnetically controlled valves and wherein the fuel in the common rail is used for the operation of the various decompression valves. This permits a free selection of the braking power since the opening and closing points of the decompression valves can be controlled while no fuel is admitted to the injectors. The fuel pressure in the common rail remains essentially constant so that high pressure fuel is always available for supply to the injectors or for operation of the decompression valves.
It is the object of the present invention to provide an improved motorbrake system wherein, over the whole operating range of an engine, a braking power can be achieved which is freely selectable so as to be optimally adapted to prevailing conditions and wherein the operating pressure of the fuel can be optimized for motorbrake operation or for normal engine power operation.